This invention relates to a method of casting beneficiation, i.e., removing undesirable surface material from castings, and more particularly to the removal of such material through impingement on the casting surface of an abrasive-containing water jet.
In steel foundry practice, even under the best controlled conditions, surface defects occur. Where the surface has to meet certain tolerances -- as for providing a bearing surface, or has to evidence a sheen -- as in the case of stainless steel castings, it has required arduous grinding to remove the defective surface material. Three general types of defects are prevalent: sand burn-in resulting from the surface metal taking up minute particles of the molding sand, scale resulting from surface oxidation incident to heat treating, and adherence of crushed core and molding sand in highly inaccessible places -- such as for locking pins and the like.
In the past it has been necessary to equip a steel foundry artisan with a grinder to work on occasions for hours to remove the defective material from the casting -- and even then the removal might not be complete. For these jobs the usual expedients of shot impingement "wheelabrating" or sand blasting were inadequate.
It was well known that metal such as steel could be cut through the use of abrasive-containing high pressure jets, i.e, operating at pressures above 30,000 psi (2000kg/cm.sup.2). However, such jets have not proved attractive to foundry art workers because of their high cost -- particularly the cost of the intensifiers needed for developing the high pressure. It was also known that metal could not be economically cut with the commonly employed low pressure jets, i.e., those operating in the range of 8,000 psi (550kg/cm.sup.2) to 12,000 psi (850kg/cm.sup.2) -- and this was irrespective of whether abrasive was employed or not. Therefore, it was most surprising to discover that a low pressure abrasive-augmented water jet operating under certain conditions possessed the selective capability of removing integral, deteriorated metal from a casting and in times which were a minor fraction of the previously known grinding times. The important operating conditions include sizing the jet-providing nozzle to deliver from about 10 gallons per minute (38 liters/min) to about 12 gallons per minute (45 liters/min) of water containing from about 5 lbs/min (2.2 kg/min) to about 7 lbs/min (3.2kg/min) of a specific abrasive -- the most useful economically being garnet sand passing an SAE size 14 screen.